The present invention relates to light distribution and light emitter cooling features for light fixtures, and particularly, to providing a light fixture with selectable locations, orientations, and quantity of light emitters.
A single light housing design can be used to provide a number of light fixtures providing different lighting features by changing various features of the fixture other than the housing. For example, in incandescent and fluorescent light fixtures, variations in fixtures with the same housing are sometimes provided by using a variety of bulb wattages or quantities, or by including an adjustable reflector and/or shade that varies the light distribution pattern.
Managing the temperature of light sources in a light fixture is generally important to performance and longevity. This is particularly true with newer highly efficient lighting technology, for example, light sources such as LEDs, laser diodes or other light emitters. LEDs are generally selected to maximize the light output for a given power consumption at a reasonable cost. Because LED light sources operate at a much lower temperature than typical incandescent light sources, less energy is wasted in the form of heat production. However, LEDs tend to be more sensitive to operating temperature and lower operating temperatures also provide a much smaller temperature difference between the LED and the ambient environment, thus requiring greater attention to thermal management to transfer and dissipate any excess heat generated by the LED driver and emitter so that the design operating temperature for the components are not exceeded.
LED light fixtures generally include both LED drivers and LED emitters. Limiting the operating temperature is most critical for the LED emitter. As temperatures rise, the efficacy of the LED is reduced, reducing the light output, and possibly reducing the lifespan of the LED. The LED emitters used in light fixtures are often in the form of an LED package, for example, a package that includes one or more LEDs, a mounting substrate, for example formed from ceramic, and optionally a lens structure.
To facilitate dissipation of heat, convection, conduction, and radiation are available modes of heat transfer. For LED light fixtures, dissipation of heat by conduction is often provided by one or more LED packages being mounted on a heat sink. The heat sink is generally integral with or thermally coupled with the light housing, which often includes external cooling fins to further facilitate the dissipation of heat by convection and radiation.
In prior art LED light fixtures, the heat sinks are often integral with the light housing so that the heat is efficiently conducted to the outside of the housing where it is then dissipated by convention and radiation; however, in such designs, it can be difficult to thermally isolate the LED driver from the LED emitters. Additionally, such an arrangement also limits the ability to provide a variety of orientations and quantities of LED emitters for a single light housing design, as each LED package is generally coupled directly to the heat sinks, and the heat sinks are generally fixed by the integral design with the housing.
In some prior art LED light fixtures, various mechanical features are used to provide selectable orientations and quantities of LED lights; however, these features can be a limitation in dissipating heat by conduction and/or can introduce unwelcome complexity and cost.
For example, to provide a selectable orientation for LED packages, one prior art design utilizes LED packages coupled by springs to mounting posts that extend from a heat sink, the elevation of the combination of springs on the posts determining the orientation of the LED package; however, this design requires heat pipes that couple the LED packages to the heat sinks. Another prior art design provides several LEDs mounted on a rotatable mounting brackets; however, the mounting bracket and rotation mechanism limits heat conduction to the external surfaces of the light housing were heat can be dissipated.
Other prior art light fixture designs include a cylindrical heat sink. The outer circumference of the cylindrical heat sink forms several flat surfaces around its circumference. Each flat surface receives one of a variety of different LED packages that can be each selected based on a desired LED intensity for the direction in which that particular LED package will be oriented. To facilitate dissipation of heat from the LEDs in this prior art design, the inside of the cylindrical heat sink forms inwardly protruding cooling fins. This cooling structure arrangement has the disadvantage that the light housing is open to the environment in order to allow air to follow through the center of the cylindrical heat sink. Additionally, the same heat sink surface and associated mass is used to receive each LED package, regardless of the amount of heat that needs to be dissipated from the particular LED package coupled to that heat sink surface and associated mass.
Therefore, it is desirable to provide a light fixture design having a single housings that can provide multiple LED configurations and appropriate heat sinks and reflectors designed for each LED configuration.